In current implementations for calculating a data-based function model in a control unit, a value for an output variable is calculated for a certain number of input variables, i.e., an input variable vector of a certain dimension. For many applications, however, it is advisable to calculate not just one but multiple values of the output variable for a varying input variable of the input variable vector. In other words, one input variable is varied and the corresponding variation in the output variable is ascertained. This may be used in particular when an inversion of the data-based function model is to be used, i.e., when a corresponding change in one of the input variables is to be deduced when an output variable is predefined.